The present invention relates to an electric resistance heating assembly, provided with heating resistances embedded in ceramics material strips coupled to one another, effective to be particularly used for plastics material extruder apparatus.
As it is known, the plastics material extrusion method comprises a step of plasticizing the material by means of heat provided from the outside and/or developed in the material itself due to the inner friction caused by the mechanical working.
It is also known that the mentioned outside heat is generally supplied by heating electric resistances, which are suitably designed and encompass the extruder barrel.
More specifically, said heating resistances consist conventionally of a number of coiled wires, having a given ohmic resistance and passing through a cross hole as formed in ceramics material strip members.
The latter, in particular, are so shaped at two opposite walls thereof, in such a way as to be able of being mutually coupled thereby providing a structure which may be evenly bent, such as an annular band, which, on its outside, is restrained by a collar member.
The mentioned ceramics material strips have a constant length and are arranged in such a way as to form, in a single assembly, two or more parallelly extending ring members, which are conveniently spaced from one another.
On the other hand, the disclosed arrangement does not afford the possibility of precisely adjusting the heat supplied to the extruder, with consequent degradations of the plastics material.
In fact, as the process starts, it is necessary to supply the extruder with excess heat, in order to provide the material itself with a suitable fluidity; the operation of the known temperature adjusting devices, on the other hand, is not of a satisfactory accuracy, even due to the high thermal inertia of the assembly.
Accordingly, the overall assembly is presently enclosed in a jacket, effective to provide a perimetrical gap wherein cooling air is caused to circulate.
However, that approach is not completely satisfactory, since it is not capable of evenly distributing heat to the extruder apparatus.